The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to a dual frequency, wideband resonator element providing at least one adjustably tuned component.
Recent advances in wireless communications devices have renewed interest in antennas suitable for such systems. Several factors are usually considered in selecting an antenna for a wireless telecommunications device. Significant among these factors are the size, VSWR, gain, bandwidth, and the radiation pattern of the antenna.
Currently, monopole antennas, patch antennas and helical antennas are among the various types of antennas being used in wireless communications devices. These antennas, however, have several disadvantages, such as limited bandwidth and large size. Also, these antennas exhibit significant reduction in gain at lower elevation angles (for example, 10 degrees), which makes them undesirable in some applications.
As mentioned above, one type of antenna is an external half wave single or multi-band dipole. This antenna typically extends or is extensible from the body of a wireless communication device in a linear fashion. Because of the physical configuration of this type of antenna, electromagnetic waves radiate equally toward and away from a user. Thus, there is essentially no front-to-back ratio and little or no specific absorption rate (SAR) reduction. Specific absorption rates for this type of antenna are typically 2.7 mw/g at a 0.5 watt transmission power level. With multi-band versions of this type of antenna, resonances are achieved through the use of inductor-capacitor (LC) traps. With this antenna, gains of +2 dBi arc common. While this type of antenna is acceptable in some wireless communication devices, it has drawbacks. One significant drawback is that the antenna is external to the body of the communication device. This places the antenna in an exposed position where it may be easily damaged.
A related antenna is an external quarter wave single or multi-band asymmetric wire dipole. This antenna operates much like the aforementioned antenna, but requires an additional quarter wave conductor to produce additional resonances. This type of antenna has drawbacks similar to the aforementioned antenna.
A dual band antenna assembly for use in a wireless communications device (WCD) is disclosed. The antenna assembly provides simultaneous wideband resonances over two or more different frequency bands when disposed relative to a ground plane of the wireless communications device. One or more of the operational frequency bands of the antenna assembly may be selectively adjusted via a capacitive tuning network. The selective adjustment of the capacitive tuning network may be achieved during the manufacture or subsequent use of the wireless communications device. In this manner, a tuning process over a much wider range of frequencies in each band may be achieved without an alteration of the physical size or structure of the antenna element. The selectively tunable antenna according to the present invention permits a single mechanical embodiment to accommodate a variety of different frequency bands, thus providing a manufacturing and assembly economy over prior art antennas (where timing has typically required an alteration of the physical structure of the antenna, or selection from among a plurality of differently sized antenna elements). The selective tuning of the antenna assembly of the present invention may be achieved via a variety of automatic or manual approaches. In one embodiment, the capacitive tuning network, such as a varactor, may be electrically tuned via the WCD microprocessor in response to an internal program or one or more external signals. In another embodiment, the capactive tuning network may be controlled via a manual operated switch, such as through a PIN diode switching device.
The antenna assembly includes first and second conductive surfaces disposed relative the ground plane of the WCD, preferably at the upper rear portion of the WCD. The first and second conductive surfaces are in substantial collateral relation and include a conductive bridge element disposed therebetween. The first and second conductive surfaces are also operatively coupled together via a capacitive tuning network, as further described herein. A conducting feed element operatively connects the first conductive surface to a signal line of the WCD. The feed element includes a feed arm defining a 50 ohm feed point. The first conductive surface is further coupled to the ground plane of the WCD via a grounding element.
In another embodiment, the antenna assembly is spaced a predetermined distance from the ground plane of a printed wiring board, and is operatively connected thereto at several predetermined locations by several components. One component, a capacitor or tuning network, capacitively couples the second conductive surface to the ground plane. Another component, the feed point of the antenna, operatively couples the first conductive surface to the RF input/output port or terminal of the WCD. Additionally, a third component, a grounding element, operatively connects the second radiating element to the ground plane. Since the distance between the antenna assembly and the ground plane is a function of the particular frequencies or wavelengths in use, the space between the antenna assembly and the ground plane may vary depending on the frequency band desired. However, it will be appreciated that various componentry may be positioned within the open space(s) between the antenna assembly and the ground plane to facilitate compact construction.
It is an object of the present invention to provide an antenna assembly which may be incorporated within the interior of a wireless communication device.
It is an object of the present invention to enhance operation of an antenna assembly by increasing its operational bandwidths and performance thereof.
It is another object of the present invention to provide an antenna assembly exhibiting at least one major polarization and one minor polarization.
Yet another object of the present invention is to provide a multiple band antenna for wireless communications devices that exhibits lower specific absorption rate (SAR) as compared to typical external antennas.
It is another object of the present invention to provide a multiple band antenna assembly wherein at least one of the frequency bands is selectively tunable by manual control or electrically tunable variable capacitor element.
It is yet another object of the present invention to provide a control assembly for adjusting the capacitance of the electrically tunable variable capacitor element, such as a digital control structure.
It is another object of the present invention to provide a variable capacitor element control assembly which is responsive to external signals received from the wireless communications system.
It is yet another object of the present invention to provide a variable capacitor element control assembly which is response to internal signals of the wireless communications device.
A feature of the present invention includes the provision that one or more portions of the resonator elements of the antenna assembly are tunable over a broad range of frequencies.
Another feature of the present invention includes the provision of a single feed point for a multi-band antenna system. The multiple band antenna assembly according to the present invention may exhibit a VSWR of approximately 2:1 over two different frequency bands, such as 880-960 MHz and 1710-1880 MHz or 824-894 MHz and 1850-1990 MHz. These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings.